Traffic control system for railroads



.[une 1-; 1937. R. M. PHlNNEY TRAFFIC CONTROL SYSTEM FOR RAILROADS IOriginal Filed June 26, 1930 A a 0mm LN INVENTOR WATTORNIIEY PatentedJune 1, 1937 UNITED STATES PATENT OFFICE TRAFFIC CONTROL SYSTEM FORRAILROADS Application June 26, 1930, Serial No. 463,940 Renewed October26, 1932 26 Claims.

This invention relates to systems and devices employed in the control ofrailroad track switches, and more particularly pertains to time elementmeans for use in such systems.

Where a track switch and the signals governing traffic thereover areunder the control of an operator, it is necessary to provide meanspreventing that switch from being operated to a new position, if agoverning signal is cleared. l However, it is highly desirable that suchcleared signal may be put to stop at any time the operator so desires,so that an on-coming train may be stopped, if possible, to allow theoperator to change the route set up. But, if the on-coming l5 train isunable to stop within the approach to the signal that was formerlycleared but which is now at stop, it is dangerous to operate the trackswitch as soon as such signal has been returned to a stop indication.

Such conditions are adequately provided for if a suitable time period isrequired between the returning of a governing signal to stop and thetime at which the track switch may be operated, as this time period iseither sufiicient for the 25 on-coming train to stop Within the approachto the formerly cleared signal, or to pass onto the switch at which timeother locking means is actuated by the train to prevent operation ofthat track switch.

With the above and other considerations in mind, it is proposed inaccordance with the pres ent invention to provide means normally causinga lapse of a predetermined time between the returning of a signal tostop and the operation of 35 the track switch associated therewith, thispredetermined time being measured by means including a thermal timeelement device which requires substantially the same length of time foreach operation regardless of the interval between successive operations.

It is further proposed to provide simple and safe means for restoringthe control of the track switch to the operator immediately after thepassage of a train, without the intervening of the usual time period.

Various other features, objects and advantages of the present inventionwill be in part obvious from the accompanying drawing, and in partpointed out as the description of the invention progresses.

The accompanying drawing illustrates in a simplified and diagrammaticmanner one form that the present invention may assume, the parts andcircuits being shown more with the object 55 of making it easy tounderstand the principles and mode of operation of the invention, thanwith the purpose of illustrating the detailed con struction of thevarious devices involved and the circuit organization preferablyemployed in practice.

With reference to the drawing, a stretch of single track comprisingrails 5 has been shown having a diverging route or passing sidingcomprising rails 6 connected thereto through a suitable track switch TS.This track switth TS is indicated as being operated'by a suitable switchmachine SM, such for example as shown in the patent to W. K. Howe,Patent No. 1,466,903, dated September 4, 1923, the control of saidswitch machine being accomplished by an operator located at someconvenient point, such switch machine control means being indicated bythe dotted rectangle SMC connected by a dotted line to the switchmachine SM, but it is to be understood that the track switch TS may beoperated in any other suitable manner.

The traflic in an east bound direction over the track switch TS isgoverned by signals l and LA for respectively governing traflic over themain track or the passing siding; similarly, the signals 2 and 2A areprovided for respectively governing trains in a west bound directionover the track switch TS from the main track or the passing siding.These signals 'l-|A and 2--2A may be controlled by the operator at aconvenient point by any suitable means, such signal control meansrepresented by the dotted rectangle SGC connected by a dotted line tothe respective signals. This manual control is preferably interrelatedwith the usual automatic control governed in accordance with traflicconditions along the right of way in a manner to cause these signals togive stop indications automatically upon the presence of a train incertain portions of the track, all in accordance with the usual practiceemployed for semi-automatic signals in interlocking plants, or inaccordance with remote control systems of the type disclosed in thepending application of S. N. Wight, Ser. No. 120,423, filed July 3,1926. It is to be understood that these signals may be of the lightsignal type but have been shown for convenience as being of thesemaphore type. Each signal is provided with suitable contacts which areclosed only when the corresponding signal is giving a stop indication.

Associated with the track switch TS is the usual detector track sectionhaving a battery B and a track relay T controlled in the usual manner. Atrack instrument TI is provided preceding the track switch to provide acheck upon the track mal conditions (as shown) when the train is notpresent to furnish such actuation. Such a track instrument, however, ispreferably of the type which requires the heavy stresses to actuate itthat can only be exerted by a train, which protects it from falseactuation by a hand car, workman or the like. 1

A lock relay L is provided having a front contact included in the commonoperating wire of the switch machine SM which is thus prevented frombeing operated by the operator at such times that this look relay is notenergized. Should the track switch TS be operated by some other suitablemeans than a power operated switch machine, such for example, as amechanical lever and pipe line, suitable locking means would. beprovided to prevent the operation of the switch, this locking meansbeing released only when the lock relay L is energized, it beingunderstood of course that'the locking means shown is merely illustrativeof one manner in which the lock relay L prevents manual operation of thetrack switch from a remote point.

A relay M is provided to indicate when the signals llA and 2-2A are atstop, any one of which signals if cleared will cause the relay M to bedeenergized. Also, a stick relay S is provided to register the actuationof a time element relay TE, and to accomplish such other functions asare hereinafter pointed out. These relays L, M and S are conventionallyshown as relays having neutral armatures, and may be of any suitableelectromagnetic type.

The time element relay TE is of the thermal relay type, such forexample, as shown in the application of J. Willi No. 463,963, filed June26, 1930, entitled Thermal relay. This relay TE includes a bi-metallicelement l2 which is actuated by a heating coil i l from its normalextreme position to the opposite extreme position during a predeterminedtime period when the heating coil is energized with a given current.This bi-metallic element is also preferably provided with compensatingmeans to allow for the variations in the room temperature in which it islocated, so that the period of time required for the element 92 to beactuated by a given our rent flowing in the coil i l to an oppositeextreme position, and the period of time required for this element 52 toreturn to its former extreme position after the heating coil it isdeenergized, shall each respectively be substantially the same for eachoperation. A resistance R is provided to allow adjustment of the currentvalue flowing in the energizing circuit of the relay including theheating coil 54. At one end of the heating element i2 is an insulatingblock G at-- tached thereto, for suitably actuating movable contacts 56and l! which are adapted to respectively engage fixed contact is or it,when the bi-metallic element i2 is in a normal extreme position or in anenergized extreme position.

The relay M is normally energized when the signals l- |A and T-2A are atstop through a circuit from the positive terminal of a suitable sourceof electrical potential indicated as through contact of signal 2, wire2|, contact 22 of signal 2A, wire 23, contact 24 of signal IA, wire 25,contact 26 of signal I, wire 27, winding of relay M, to the oppositeterminal of the suitable source indicated as Assuming that the signalsl-IA and 22A are at stop, and that, either a train has passed to restorethe devices to normal conditions, or sufficient time has lapsed torestore the devices to normal positions, the lock relay L is energizedfrom the positive terminal of a suitable source of electrical potentialindicated as through fixed contact l8 of thermal relay TE, movablecontact l6, wire 30, front contact 3| of stick relay S, wire 32, frontcontact 33 of track relay T, wire 34, closed contact H of trackinstrument TI, wire 35, winding of lock relay L, to the oppositeterminal of the suitable source indicated as Also; with the circuitarrangement and devices in the conditions as shown, the stick relay S isenergized through a circuit from the positive terminal of a suitablesource of electrical potential indicated as through wire 38, heatingcoil i i of thermal relay TE, adjusting resistance R, wire 39, frontcontact 430 of relay S, wires 4! and 412, winding of relay S, wires 43and M, front contact 45 of relay M, to the opposite terminal of thesuitable srfirce indicated as Although sufhcient current flows in thiscircuit to maintain the contacts of the stick relay in actuatedpositions, this current is insuihcient to appreciably heat the thermalele-' ment of the relay TE.

It is to be understood, that if the thermal element of the relay TE isadjusted to be actuated on such a small value of current that thiscurrent in the stick circuit of the relay S becomes objectionable, afront contact may be included in the stick relay S, in a manner todirectly provide positive energy to wire 4| when the relay is energized,while back contact 49 will still be employed to control the energizationof relay TE as shown.

Let us now assume that the operator clears one of the signals throughthe signal control means SGC, such for example as signal 2, then thecontact 20 is operated to an open position thereby deenergizing therelay M. This deenergization of the relay M opens the stick circuit forthe stick relay S at front contact %5 causing its contacts ill and ll]to assume deenergized positions which in turn open the energizingcircuit for the lock relay L at front contact 3|. The deenergization ofthe lock relay L opens the common control 'wire of the switch machine atfront contact 50, so that the operator cannot operate the track switchTS through the switch machine control means SMC.

If the operator now decides to return the signal 2 to a stop positionand then operate the switch machine to a reverse position, to allow'atrain to move off the passing siding, then the contact 28 is closed andthe relay M is then energized in response thereto, but the switchmachine does not respond to the manual control SMC until the relay L isenergized.

The energization of the relay M closes an energizing ci cuit for theheating coil H! of the thermal relay TE" from the positive terminal ofthe suitable source of electrical potential indicated as through wire38, heating coil l4,

adjusting resistance R, wire 39, back contact 16 of relay S, wires 4?and 44, front contact 45 of relay M, to the opposite terminal of thesuitable source indicated as After a predetermined time the bi-metallicelement i2 is actuated to a left hand position to actuate the movablecontact ii to engage the fixed contact Hi. This closes a pick-up circuitfor the stick relay S from the positive terminal of a suitable source ofelectrical potential indicated as through movable contact ll, fixedcontact 99, wires 48 and d2, winding of relay S, wires 43 and M, frontcontact 45 of relay M, to the opposite terminal of the suitable sourceindicated as As soon as the contacts of relay S are actuated toenergized positions, the energizing circuit for the heating element ofrelay TE is opened at back contact Gil of the relay S, while this frontcontact of relay S closes its stick circuit as heretofore traced. As thecurrent which now flows in the stick circuit is of insufficient value toeffect the heating coil i i of relay TE, the bi-metallic element returnsto its normal position after a predetermined time.

With the stick relay S now energized and the thermal relay TE in anormal non-actuated position, the energizing circuit for the lock relayL is completed, which permits the response of the switch machine SM tothe switch machine control SMC. Thus, the switch TS is prevented frombeing manually controlled for a predetermined time period after anygoverning signal is put to stop, this time period including the heatingand cooling time of the thermal element 52 of relay TE (required tosuccessively close'its front and back contact).

Let us assume that the operator now controls the track switch TS to areverse position after which he clears the signal 2A. The relay M isdeenergized by the opening of contact 22 and prevents further operationof the switch machine SM except, as heretofore explained, after thesignal 2A is returned to normal. But, assuming that while the signal 2Ais cleared, a train passes over the track switch TS onto the main trackin ac cordance with the signal 2A, the track relay T is deenergized dueto the shunting of the detector track circuit, and the track instrumentTI is actuated by the presence of the train in a manner to close contactid and to open contact II. Also, with the detector track circuitoccupied, the signal 2A is put to stop by automatic means (not shown)thereby closing the circuit for the relay M. As the track relay T isshunted, the circuit for the relay L is opened at front contact 33 oftrack reiay T; also, as the track instrument is actuated, the contact Hof the track instrument TI is open. This double opening of the circuitof the relay L insures that the switch machine cannot be operated by theoperator during the presence of a train upon the detector track section.

The presence of the train is also employed to energize the stick relay Swithout the actuation of the relay TE. This energizing circuit is tracedfrom the positive terminal of a suitable source of electrical potentialindicated as (-1-), closed contact iii of track instrument TI, backcontact 52 of relay T, wires 53 and 52, winding of relay S, wires 4-3and d4, front contact 35 of relay M, to the opposite terminal. of thesuitable source indicated as The energization of the stick relay Sthrough this pick-up circuit causes the contacts of the relay S toassume energized positions closing its stick circuit as heretoforetraced.

As soon as the train moves off the track section closing the frontcontact 33 of track relay T and the contact H of track instrument TI,the circuit for the relay L will then be completed as heretofore tracedallowing the switch machine SM to be immediately operated in response tooperation of the manual switch machine control SMC.

From the above description, it is obvious that when the time elementrelay TE is employed to release the locking means of the switch machineSM, its thermal element is first heated and then cooled in order todetermine or measure the time intervening between the putting to stop ofa signal and the operation of the switch machine. In other words, theactuation of the time element relay is registered by the stick relay S,which then deenergizesthe time element relay returning it to normal,after which the switch machine SM may be operated. This arrangementprovides that the switch machine is not unlocked until the time elementrelay TB is returned to a normal position in readiness for its nextoperation thereby insuring that the time period marked off or measuredby the thermal time element relay of this invention is alwayssubstantially the same regardless of the number or the frequency of itssuccessive operations. This is true as the cooling time period of thethermal element for each operation is included in the time periodmeasured off, which prevents the thermal element from ever being heatedan appreciable value above room temperature when in a normal position,thereby providing substantially the samerelative starting point for eachoperation.

It is also seen from the above description, that should the detectortrack circuit become accidentally shunted by a track crew or opencircuited by the breaking of a bond wire, the locking of the trackswitch TS will not be falsely released, as the presence of a train isrequired to actuate the track instrument. Similarly, the converse istrue in that the track instrument cannot for some erroneous reasonfalsely unlock the track switch TS as the shunting of the detector trackcircuit is required in conjunction therewith. Thus, one specificembodiment of the present invention is shown and described as applied toa railroad track switch, but it is to be understood that the inventionis not limited to this particular application or to the particularstructure and arrangement of parts and circuits shown and described, butvarious additions, modifications and adaptations of the specificembodiment of the present invention may be made all in accordancetherewith without departing from the scope thereof except as demanded bythe scope of the appended claims.

What I claim is:

1. In a traffic controlling system for railroads, a power operated trackswitch, signals governing traffic over said track switch, a time elementdevice temporarily actuated each time when said signals are put to stop,means registering the temporary actuation of said time element device,and means preventing the operation of said track switch except when saidtime element device has returned to normal after registering a temporaryactuation.

2. In a trafiic controlling system for railroads, a power operated trackswitch, signals governing trafiic over said track switch, a time elementdevice temporarily actuated each time said signals are put to stop,means registering the temporary actuation of said time element device,means a1- lowing the operation of said track switch only.

when said time element device has returned to normal after registering atemporary actuation, and means cancelling said registering means whensaid signals are clear.

3. In combination, a power operated track switch, a signal governingtraific over said switch, a lock relay acting while deenergized toprevent operation of said switch, a stick relay, a pick-up circuit forsaid stick relay governed by said signal and traflic conditions adjacentsaid signal, a stick circuit governed by said signal, a time elementdevice, means actuating said time element device when said stick relayis deenergized and said signal indicates stop, a second pick-up circuitfor said stick relay closed when said time element device is actuated,and a circuit energizing said lock relay closed only when said stickrelay is energized and said time element device is in its non-actuatedcondition.

4. In a control system for railroads, a track switch, signals governingtraflic over said track switch, locking means normally effective toprevent operation of said track switch for a predetermined time aftersaid signals are caused to indicate stop. a detector track sectionhaving a track relay, a track instrument in said detector track section,and means causing said locking means to be ineffective to preventoperation of said track switch if both said track relay and said trackinstrument indicate the presence of a train.

5. In combination, a track switch, signals governing trafiic over saidswitch, locking means normally effective to prevent operation of saidtrack switch for a predetermined time after said signals indicate stop,a detector track section having a track relay, a track instrument insaid detector track section, means preventing operation of said trackswitch when either said track relay or said track instrument indicatethe presence of a train, and means causing said locking means to bereleased if said track relay and said track instrument indicate thepresence of a train.

6. In a control system for railroads, a track switch, signals governingtraffic over said switch, manual control means for said switch and saidsignals, a detector track section having a track relay, a trackinstrument physically engaged by a train passing said track switch, andmeans causing said manual control means to be ineifective to operatesaid track switch and said signals when said track relay and said trackinstrument indicate the presence of a train.

- '7. In a control system for railroads, a track switch, signalsgoverning traffic over said switch, manual control means for said switchand said signals, a detector track section having a track relay, a trackinstrument physically actuated by a train passing said track switch,locking means preventing manual control of said switch for apredetermined time after said signals have been put to stop, automaticmeans for putting said signals to stop, and automatic means releasingsaid locking means if said track relay and said track instrumentindicate the presence of a train and said signals have been put to stop.

8. In combination, a power operated track switch, a signal governingtraffic over said switch, a lock relay acting while deenergized toprevent operation of said switch, a stick relay, a pick-up circuit forsaid stick relay governed by said signal and traffic conditions adjacentsaid signal, a stick circuit governed by said signal, a time elementdevice, means actuating said time element device when said stick relayis deenergized and said signal indicates stop, a second pick-up circuitfor said stick relay closed when said time element device is actuated,and a circuit energizing said lock relay when said stick relay isenergized and said time element device is not in its actuated condition.

9. In combination, a track switch, manually controllable means forgoverning operation of said track switch, a track circuit associatedwith said track switch including a track relay, a track instrumenthaving contacts operated by the passage of a train and located in thesection of said track circuit, locking means for locking said trackswitch against operation, and means for releasing said locking meanseffective upon temporary presence of a train as manifestedsimultaneously by said track relay and said track instrument.

10. In combination, a track switch, manually controllable means forgoverning operation of said track switch, a track circuit associatedwith said track switch including a track relay, a track instrumenthaving contacts operated by the passage of a train associated with saidtrack switch, locking means for locking said track switch againstoperation, a stick relay, a pick-up circuit for said stick relay closedonly if a train is manifested simultaneously by said track relay andsaid track instrument, and a circuit for rendering said locking meansineifective including in series a front contact of said stick relay andnormally closed contacts controlled by said track relay and said trackinstrument.

11. In combination, a track switch, manually controllable means forgoverning operation of said track switch, a signal associated with saidtrack switch, a track circuit associated with said track switchincluding a track relay, a track instrument having contacts operated bythe passage of a train associated with said track switch, locking meansfor locking said track switch against operation, a stick relay, apick-up circuit for said stick relay closed only if said signal is atstop and a train is manifested simultaneously by said track relay andsaid track instrument, and a circuit for rendering said locking meansineffective including in series a front contact of said stick relay andnormally closed contacts controlled by said track relay and said trackinstrument.

12. In combination, a track switch, manually controllable means forgoverning operation of said track switch, a signal associated with saidtrack switch, a track circuit associated with said track switchincluding a track relay, a track instrument having contacts operated bythe passage of a train and associated with said track switch, lockingmeans for locking said track switch against operation, and means forreleasing said locking means eifective upon temporary presence of atrain as manifested simultaneously by said track relay and said trackinstrument providing said signal is then at stop.

13. In combination, a section of railway track, a switch associated withsaid section, a switch lock relay for controlling the operation of saidswitch, a track circuit in said section including a track relay, a timeelement relay for controlling the operation of said switch lockingrelay, manually controlled means for controlling the operation of saidtime element relay, and a circuit for said locking relay including inseries a front contact of said track relay and a track device contactseparate from said track circuit and opened only by the presence of atrain in said section.

14. In combination, a section of railway track, a track switch in saidsection, a switch machine for operating said switch, a signal governingthe movement of trafiic over said track switch, a stick relay which mustbe energized to permit control of said switch machine, a track circuitextending the entire length of said section and including a track relay,a track device in said section which by physical actuation by said trainmanifests the presence of a train in said sec-- tion, a pick-up circuitfor said stick relay including in series a back contact of said trackrelay and a normally open contact of said track device, and a stickcircuit for said stick relay closed only if said signal is at stop.

15. In combination, a section of railway track,

a track switch in said section, a switch machine for operating saidswitch, a signal governing the movement of traffic over said trackswitch, a stick relay which must be energized to permit control of saidswitch machine, a track circuit extending the entire length of saidsection and including a track relay, a track device in said section butseparate from said track circuit to manifest the presence of a train insaid section, a pick-up circuit for said stick relay including in seriesa back contact of said track relay and a normally open contact of saidtrack device, a stick circuit for said stick relay closed only if saidsignal is at stop, another relay having control contacts in theenergizing circuit for said switch machine, and an energizing circuitfor said another relay including a front contact of said stick relay, afront contact of said track relay and a normally closed contact of saidtrack device.

16. In combination with a section of railway track, a railway switch insaid section, a track relay for said section, a signal governing trafiicthrough said section. a circuit controller associated with said sectionand normally occupying one position, means independent of said trackrelay for causing said circuit controller to be operated to anotherposition by a train occupying the section, locking means effective toprevent operation of said switch for a measured time interval after saidsignal is moved to the stop position, and means requiring said trackrelay to be deenergized and requiring said circuit controller to occupysaid other position for releasing said locking means.

17. In combination, a section of railway track including a track switch,an approach locking relay, a track relay for said section, auxiliarymeans for detecting the presence of a train in said section, a pick-upcircuit for said approach locking relay closed only when the track relayis deenergized and said auxiliary means indicates the presence of atrain in said section, and a control circuit for the switch closed onlywhen the approach locking relay and the track relay are energized, andsaid auxiliary means indicates that no train is present in said section,and manually controllable means rendered effective to operate the switchonly when said control circuit is closed.

18. In combination, a section of railway track including a track switch,an approach locking relay, a track relay for said section, auxiliarymeans for detecting the presence of a train at a particular pointadjacent said switch, a pick-up circuit for said approach locking relayclosed only when the track relay is deenergized and said auxiliary meansindicates the presence of a train at said point, and a control circuitfor the switch closed only when the approach locking relay and the trackrelay are energized and said auxiliary means indicates that no train ispresent at said point, and manually controllable means effective tooperate the switch only when said control circuit is closed.

19. In combination, a section of railway track including a track switch,an approach locking stick relay, means for preventing operation of saidswitch unless said relay is energized, a signal for governing themovement of traffic over the switch, a track circuit including a trackrelay connected across the rails of said section, auxiliary meansindependent of said track circuit for detecting the presence of a trainin said section, a pick-up circuit for said approach locking relayclosed only when the signal indicates stop, the track relay isdeenergized and. said auxiliary means indicates the presence of a trainin said section, and a stick circuit for said approach looking relayincluding a front contact of said relay and closed only when the signalindicates stop.

20. In combination, a section of railway track, traiiic governing meanslocated in said section, a track relay for said section, a circuitcontroller located in the trackway adjacent said traiiic governingmeans, means independent of said track relay for causing said circuitcontroller to occupy one position under normal conditions but to occupyanother position when a train occupies said section, a manuallycontrolled relay, circuits including contacts of said manuallycontrolled relay for controlling the operation of said traffic governingmeans, and a circuit for said manually controlled relay including afront contact of said track relay and a contact of said circuitcontroller closed only in said one position.

2.1. In combination, a section of railway track, a track switch in saidsection, a track relay for said section, a circuit controller associatedwith said section and normally occupying one position, means independentof said track relay for causing said circuit controller to be operatedto another position by a train occupying the section, a switch lockingrelay for governing the operation of said switch, a circuit for saidswitch locking relay including a back contact of said track relay and acontact of said circuit controller closed only in said other position,and a manually controlled time element relay for controlling said switchlocking relay.

22.. In combination, a section of railway track including a trackswitch, an approach locking relay, a track circuit including a trackrelay connected across the rails of said section, auxiliary meansindependent of said track circuit including a normally open contactclosed only when a train enters said section and a normally closedcontact opened only when a train enters said section, a pick-up circuitfor said approach locking relay including in series said normally opencontact and a back contact of said track relay, and a control circuitfor said switch including in series said normally closed contact andfront contacts of said track relay and of said approach locking relay.

23. In combination with a section of railway track including a trackswitch, a track relay for said section, a circuit controller associatedwith said section and normally occupying one position, means independentof said track relay for causing said circuit controller to be operatedto another position by a train occupying said section, locking means andoperating means for said switch, means requiring said track relay to bedeenergized and requiring said circuit controller to occupy said otherposition for releasing said locking means, and means requiring saidtrack relay to be energized and requiring said circuit controller tooccupy said one position for rendering said operating means responsiveto the release of said locking means.

24. In combination, a section of railway track including a track switch,a signal for governing the movement of traffic into said section,approach locking means effective to prevent operation of the switch fora measured time interval after said signal is moved to the stopposition, a track circuit including a track relay deenergized when atrain is present in said section, auxiliary means independent of saidtrack circuit for detecting the presence of a train adjacent saidswitch, means for releasing said locking effective only when said trackrelay and said auxiliary means indicate the presence of a train in saidsection adjacent said switch, and manually controllable means foroperating the switch effective when said locking is released providedthe track relay and said auxiliary means indicate that said train is nolonger present in said section nor adjacent said switch.

25. In combination, a section of railway track including a track switch,an approach locking stick relay, means for preventing operation of saidswitch unless said relay is energized, a signal for governing themovement of traffic over the switch, a track circuit including a trackrelay connected across the rails of said section, auxiliary meansindependent of said track circuit for detecting the presence of a trainin said section, a pick-up circuit for said approach locking relayclosed only when the signal indicates stop, the track relay isdeenergized and said auxiliary means indicates the presence of a trainin said section, a second pick-up circuit for said approach lockingrelay including a contact closed momentarily when the signal has been inthe stop position for a predetermined time interval provided saidapproach locking relay is then deenergized, and a stick circuit for saidapproach locking relay including a front contact of said relay andclosed only when the signal indicates stop.

26. In combination, a section of railway track including a track switch,an approach locking stick relay, a signal for governing the movement oftrafiic over said switch, a track circuit including a track relayconnected across the rails of said section, means independent of saidtrack circuit including a normally open contact closed only when a trainenters said section and a normally closed contact opened only when atrain enters said section, a pick-up circuit for the approach lockingrelay closed only when said normally open contact is closed and saidtrack relay is deenergized, a stick circuit for the approach lockingrelay including its own front contact and a contact closed only whensaid signal is in its most restrictive condition, and a control circuitfor said switch including in series said normally closed contact andfront contacts of said track relay and said approach locking relay.

ROBERT M. PHINN'EY.

